With use of X-rays in the wavelength range from several nanometers to angstroms, it is possible to observe the structures of materials, electrons, and chemical bonding states, and it is also possible to observe the inside of the materials because X-rays have high transmissivity. X-rays are indispensable light in many fields of advanced science and technology such as material science and life science. In view of the above, research and development of X-ray focusing elements indispensable for high resolution microscopes have been actively carried out. Representative X-ray focusing elements are a zone plate and a KB mirror. Regarding soft X-ray focusing, a soft X-ray microscope using a zone plate and having a resolution of 10 nm has been reported (see Non-Patent Document 1). Further, in the field of hard X-ray focusing, 7 nm-focusing by using a KB mirror has been reported (see Non-Patent Document 2). However, both of the focusing performances of a zone plate and a KB mirror have reached a theoretical limit. There is a demand for a novel focusing element for further improvement of focusing performance.
A zone plate mainly used as an X-ray focusing optical element has low focusing efficiency. In addition to the above, the zone plate is usable only for a single wavelength because the zone plate utilizes a diffraction phenomenon. On the other hand, a reflective rotating mirror is an idealistic focusing element because the reflective rotating mirror has a large aperture, high focusing efficiency, and is free of chromatic aberration. For instance, Patent Document 1 discloses an X-ray focusing element provided with a rotating parabolic reflection surface or a rotating ellipsoidal reflection surface. Patent Document 2 discloses an X-ray device, in which a rotating mirror (a Wolter mirror) configured such that one of the focal points of a rotating ellipsoidal surface and one of the focal points of a rotating hyperbolic surface are made to coincide with each other is used as an X-ray focusing optical system. Nowadays, a process for manufacturing a high-precision rotating mirror incorporated with a variety of unique manufacturing techniques is being developed, and the high-precision rotating mirror will be put into practical use in the near future (see Non-Patent Document 3).
When manufacturing of a high-precision rotating mirror (such as a rotating parabolic mirror, a rotating ellipsoidal mirror, or a Wolter mirror) is completed, a facility in which great advantages are expected to be obtained is a next-generation radiation facility. An X-ray to be output with use of a high-precision rotating mirror has high luminance and is fully coherent. Therefore, it is possible to maximally obtain the performance of the focusing element. Further, it is possible to maximally utilize the performance of the X-ray by collecting the X-ray on a rotating mirror. However, the divergence angle of radiated light is very small, and it is impossible to apply the light to the entire surface of a rotating ellipsoidal mirror 1 having a large aperture. As a result, beams are collected using only a part of illumination (see FIG. 1). In view of the above, there is proposed a technique, in which a beam is expanded by an upstream mirror 2, and is collected by using the entire surface of the rotating ellipsoidal mirror 1. However, it is impossible to collect a beam traveling through the middle portion of the rotating ellipsoidal mirror 1, and the focusing intensity may decrease (see FIG. 2). As described above, in the conventional art, it is difficult to perform nano-focusing and use all the fluxes while utilizing a large numerical aperture when a rotating mirror is used.